WO2017095773A1 - Formulation d'encre composite avec hydrogel et procédé d'impression 4d d'une structure composite avec hydrogel - Google Patents

Formulation d'encre composite avec hydrogel et procédé d'impression 4d d'une structure composite avec hydrogel Download PDF

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Publication number
WO2017095773A1
WO2017095773A1 PCT/US2016/063918 US2016063918W WO2017095773A1 WO 2017095773 A1 WO2017095773 A1 WO 2017095773A1 US 2016063918 W US2016063918 W US 2016063918W WO 2017095773 A1 WO2017095773 A1 WO 2017095773A1
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filaments
hydrogel
layer
filler particles
anisotropic filler
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PCT/US2016/063918
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English (en)
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Jennifer A. Lewis
Amelia Sydney GLADMAN
Elisabetta Matsumoto
Lakshminarayanan Mahadevan
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President And Fellows Of Harvard College
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Priority to US15/779,462 priority Critical patent/US20180251649A1/en
Publication of WO2017095773A1 publication Critical patent/WO2017095773A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/14—Printing inks based on carbohydrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/106—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
    • B29C64/118—Processes of additive manufacturing using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material using filamentary material being melted, e.g. fused deposition modelling [FDM]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/30—Auxiliary operations or equipment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y70/00—Materials specially adapted for additive manufacturing
    • B33Y70/10—Composites of different types of material, e.g. mixtures of ceramics and polymers or mixtures of metals and biomaterials
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/10—Printing inks based on artificial resins
    • C09D11/101—Inks specially adapted for printing processes involving curing by wave energy or particle radiation, e.g. with UV-curing following the printing
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/38—Inkjet printing inks characterised by non-macromolecular additives other than solvents, pigments or dyes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/0058—Liquid or visquous
    • B29K2105/0061—Gel or sol
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
    • B29K2105/16—Fillers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
    • B29K2995/0037—Other properties
    • B29K2995/0044—Anisotropic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y80/00—Products made by additive manufacturing

Definitions

  • the present disclosure is related generally to ink formulations for 3D printing and more particularly to printed structures that can swell to adopt a curved shape.
  • 3D printing entails flowing a rheologically-tailored ink composition through a deposition nozzle integrated with a moveable micropositioner having x-, y-, and z-direction capability. As the nozzle is moved, a filament comprising the ink composition may be extruded through the nozzle and continuously deposited on a substrate in a configuration or pattern that depends on the motion of the micropositioner. In this way, 3D printing may be employed to build up 3D structures layer by layer.
  • Shape morphing systems form the basis for a range of
  • a method of 4D printing comprises depositing a layer of filaments in a predetermined arrangement on a flexible substrate.
  • Each filament comprises a hydrogel matrix and a plurality of anisotropic filler particles embedded therein.
  • the filaments contact the flexible substrate at one or more contact regions.
  • the layer of filaments is hydrated, and the filaments swell in size while remaining in contact with the flexible substrate at the contact regions.
  • the flexible substrate is thereby induced to adopt a predetermined curved shape.
  • each filament comprising a hydrogel matrix and a plurality of anisotropic filler particles embedded therein; depositing a second layer of the filaments in a second predetermined arrangement on the first layer, the filaments from the second layer contacting the filaments from the first layer at a number of contact regions; hydrating the first layer and the second layer, the filaments of the first and second layers swelling in size while remaining in contact at the contact regions to form a curved three- dimensional hydrogel composite structure; and after the hydrating and the swelling, exposing the hydrogel matrix to a stimulus to induce deswelling of the filaments and shape reversal to a contracted configuration.
  • a hydrogel composite ink formulation for 4D printing comprises: an aqueous suspension including: an aqueous solvent; anisotropic filler particles; clay particles; one or more monomers comprising an acrylamide and/or an acrylate; a polymerization initiator; and an oxygen-scavenging enzyme.
  • FIG. 1 is a schematic of the shear-induced alignment of
  • anisotropic filler particles in a hydrogel composite filament during extrusion of an ink formulation through a nozzle (direct ink writing).
  • FIG. 2A shows a 3D printed planar bilayer structure comprising hydrogel composite filaments prior to hydration; and FIG. 2B shows a hydrogel composite structure formed after exposing the bilayer structure of
  • FIG. 2 A to water.
  • FIG. 3 is a schematic of a portion of a hydrogel composite filament before (left image) and after (right image) swelling, where the anisotropy in the swelling along the long axis compared to the short axis is illustrated.
  • FIG. 4 is a plot showing the effect of nozzle diameter on
  • FIG. 5 is a plot comparing the swelling strain of cast and printed samples formed with a nozzle diameter of 510 microns.
  • FIGs. 6A-6C show direct images of stained cellulose fibrils in isotropic (cast), unidirectional (printed) and patterned (printed) samples, respectively, where the scale bar represents 200 microns.
  • FIG. 6D shows data obtained from Fourier analysis of the stained images to quantify the directionality; printed unidirectional samples exhibit a clear peak corresponding to the print direction, while isotropic samples show no clear directional peaks.
  • FIGs. 7A-7D show images of a 4D printed structure (90°/0° bilayer) including a stimuli-responsive hydrogel (poly(N-isopropylacrylamide; PNIPAm)) containing oriented cellulose fibrils that reversibly changes shape depending on the water temperature;
  • FIGs. 7A and 7B show respective top and side views of the hydrated structure at room temperature and
  • FIGs. 7C and 7D show respective top and side views of the planar structure obtained after exposing the hydrated structure to a warm water bath.
  • Nozzle size 250 Mm.
  • FIGs. 7E-7H show images of a 4D printed structure (90°/0° bilayer) including the same stimuli-responsive clay-based hydrogel as used in FIGs. 7A-7D; however, instead of cellulose fibrils, single-walled carbon nanotubes are employed as the anisotropic filler particles. Due to the presence of the carbon nanotubes, the reversible shape change may be effected by heat and/or infrared light.
  • FIG. 8A shows elastic modulus as a function of carbon fiber (CF) concentration as determined from tensile tests of room temperature-swollen unidirectionally aligned (longitudinal and transverse) tensile specimens.
  • FIG. 8B shows anisotropic swelling of a 3D printed solid infilled structure comprising a NIPAm-CF hydrogel as a function of CF content and temperature.
  • FIG. 9 shows the print path of longitudinal (left) and transverse (right) tensile specimens.
  • FIGs. 10A-10C show print paths (top) and final swollen 3D structures (bottom) that display positive, negative and varying Gaussian curvature, respectively, where the scale bar is 2.5 mm.
  • FIG. 1 1 A shows a complex flower morphology (right and bottom) formed by hydrating a 3D printed structure composed of 90°/0° bilayers oriented with respect to the long axis of each petal (left).
  • FIG. 1 1 B shows a complex flower morphology (right and bottom) formed by hydrating a 3D printed structure composed of -45745° bilayers oriented with respect to the long axis of each petal (left).
  • FIG. 12 shows curvature as a function of time during hydration of the 90°/0° flower bilayer.
  • FIG. 13A shows a native calla lily flower
  • FIG. 13B shows a mathematically generated model of the flower
  • FIG. 13C shows that the curvature of the flower may be extracted from the mathematically generated model
  • FIG. 13D shows the two-layer print path obtained from the curvature data and the arrangement of filaments in each layer, where printing is carried out with a nozzle size of 410 microns
  • FIG. 13E shows the 3D printed structure after hydration and consequent swelling to the
  • predetermined calla lily shape (the scale bars represent 5 mm).
  • 3D printing can be used to create hydrogel composite filamentary structures encoded with localized, anisotropic swelling behavior that can be triggered by exposure to water.
  • the local swelling behavior may be controlled by the alignment of anisotropic (high aspect ratio) filler particles along prescribed printing pathways.
  • 3D print arrangements of hydrogel composite filaments that predictably change shape when hydrated, yielding complex plant-inspired and/or other architectures. It is also possible to use a 3D printed arrangement of hydrogel composite filaments to induce a controllable shape change in an underlying flexible substrate.
  • the combination of 3D printed composite filamentary structures with programmable swelling upon exposure to water can be referred to as biomimetic 4D printing, or simply 4D printing.
  • the elastic and swelling anisotropies of a hydrogel composite filament can be influenced or determined by the orientation of stiff, anisotropic particles within the filament.
  • the embedded anisotropic filler particles may take the form of fibrils, fibers, nanotubes, nanowires, whiskers, platelets or another high aspect ratio morphology.
  • the anisotropic filler particles 108 may undergo shear-induced alignment within the hydrogel matrix 1 16 as the composite ink formulation 120 is extruded through a deposition nozzle 122, as illustrated in FIG. 1 .
  • the 3D printing process may yield composite filaments 102 with longitudinally- oriented particles 108 and a predetermined anisotropic stiffness, such that anisotropic swelling occurs along the length of the filament as defined by the print path (longitudinal direction 124) compared to the transverse direction.
  • the term “swelling strain” or “swelling” may refer to a change in length over an original length (Al/it ⁇ ) measured along a particular direction.
  • the directions of interest for the composite filaments are the longitudinal direction (which coincides with the long axis or length of the filament) and the transverse direction (which coincides with the short axis or width of the filament).
  • anisotropic swelling” or “swelling ratio” may refer to a comparison between swelling strain along the short axis (cu) and the swelling strain along the long axis (a M ) of the filament.
  • the 4D printing method may entail depositing a first layer 104 of filaments 102 on a substrate 1 14 in a first predetermined arrangement, where each filament 102 comprises a hydrogel 1 16 with anisotropic filler particles 108 embedded therein.
  • / ' may have any integer value without limit (e.g., n may be as high as 10, 10 2 , 10 3 , 10 4 , 10 5 , or 10 6 , or even higher).
  • the filaments 102 of the first and second layers 104,106 may be hydrated. The filaments 102 swell in size while remaining in contact at the contact regions X, to reach a predetermined curved shape 1 12.
  • differential swelling between the first and second layers 104,106 can induce curvature if the layers are forced to remain in contact along the interfacial region.
  • a curved 3D shape can be formed upon hydration.
  • the first and second layers 104,106 of filaments 102 have a planar arrangement 1 10 that morphs into a nonplanar curved shape 1 12 upon hydration. Due to the swelling, some or all of the space 1 18 between the as-deposited filaments 102 may be filled in after hydration, leading to the formation of a swollen 3D shape 1 12 having either no porosity or a decreased amount of porosity compared to the as-printed (pre-hydration) configuration.
  • a layer of hydrogel composite filaments 102 may be deposited in a predetermined arrangement onto a flexible substrate in order to induce a controllable shape change in the flexible substrate upon hydration of the hydrogel composite filaments.
  • the filaments may contact the flexible substrate at one or more contact regions, depending on the morphology of the flexible substrate (e.g., whether solid or porous).
  • the flexible substrate may take the form of a textile comprising natural and/or synthetic fibers.
  • the anisotropic filler particles 108 embedded in the hydrogel composite filament 102 may be at least partially aligned or highly aligned with a longitudinal axis of the filament 102, as defined below. Accordingly, the swelling of the hydrogel composite filaments may be greater along the transverse axis (or short axis) than along the longitudinal axis (or long axis), as illustrated in FIG. 3. Data indicate that 3D printed filaments including high aspect ratio particles with high alignment along the print direction may exhibit up to a four-fold difference in longitudinal and transverse swelling (e.g., respectively) as shown by the swelling strain data of FIGs. 4 and 5.
  • a ratio of the swelling along the short axis cu to the swelling along the long axis a M may be at least about 1 .5, at least about 2, at least about 2.5, or at least about 3. This ratio, which may be referred to as the "swelling ratio,” may also be as high as about 10, as high as about 6, or as high as about 4. The extent of the shear-induced
  • the magnitude of the anisotropic swelling depends at least in part on the nozzle diameter and printing speed.
  • the shear forces that promote alignment of the anisotropic filler particles may scale inversely with nozzle size.
  • Hydrating the filaments to induce swelling may entail exposing the layers to water or an aqueous solution by dipping, immersion, spraying, or another deposition method.
  • the hydrating may also or alternatively entail exposing the first and second layers of filaments to a humid environment, such as an air environment having a humidity of at least about 40%, at least about 60%, or at least about 80%.
  • the composition of the hydrogel composite ink formulation used to print the hydrogel composite filaments is critical to the success of the 4D printing process.
  • the hydrogel composite filaments may be formed from a hydrogel composite ink formulation by extrusion through a deposition nozzle.
  • the composition of the deposited hydrogel composite filaments and the hydrogel composite ink formulation extruded through the nozzle may be the same or substantially the same (allowing for, for example, some minuscule amount of evaporation or other changes during 3D printing). It is also understood that both the hydrogel composite ink formulation and the hydrogel
  • composite filaments prior to polymerization, comprise an uncured hydrogel that may be defined in terms of the constituent monomer(s).
  • hydrogel or “hydrogel matrix” may be used in reference to both uncured and cured (or crosslinked) hydrogels throughout this disclosure.
  • the hydrogel composite ink formulation may include one or more monomers comprising an acrylamide and/or an acrylate, anisotropic filler particles, clay particles, a polymerization initiator, and an oxygen- scavenging enzyme in an aqueous solvent.
  • the one or more monomers are polymerized to form a hydrogel matrix that readily swells upon exposure to water.
  • the clay particles may serve as a crosslinker for the monomer(s) as well as a rheological aid in the ink composition that promotes the
  • the oxygen-scavenging enzyme can scavenge ambient oxygen, which can otherwise inhibit or prevent polymerization of the monomer(s) during curing.
  • the anisotropic filler particles may serve as stiff reinforcements with an elastic modulus (E) in excess of 100 GPa and/or exhibit other functionalities, such as electrical conductivity, photothermal activity, bioactivity and/or magnetic properties.
  • the aqueous solvent may comprise the balance of the ink formulation considering the concentrations of the other components as set forth below.
  • hydrogel composite filaments may include stiff cellulose fibrils embedded in an acrylamide matrix, which mimics the composition of plant cell walls.
  • the hydrogel composite filaments may be 3D printed from ink formulation comprising an aqueous suspension of N,N- dimethylacrylamide (or N-isopropylacrylamide for reversible systems, as discussed below) along with nanofibrillated cellulose (NFC) and a
  • the aqueous suspension may also include clay particles, glucose oxidase and glucose, as discussed below.
  • 3D printed hydrogel composite filaments exhibit a clear peak at 0°, corresponding to the print direction, while the isotropic samples show no clear directional peaks.
  • the monomer(s) may be polymerized to form a crosslinked hydrogel matrix.
  • the polymerization entails
  • the polymerization initiator used in the composite ink formulation may be a photoinitiator, such as Irgacure® 2959 from BASF Corp.
  • Photopolymerization may be carried out by exposing the hydrogel composite filaments to UV light for a time duration ranging from 5 seconds to about 10 minutes. Typically, the time duration is from about 1 minute to about 3 minutes.
  • the monomer(s) may be physically cross-linked by the clay particles during polymerization, thereby increasing the mechanical strength of the hydrogel matrix.
  • Recent modeling suggests that an increase in clay content may result in an increase in the formation of interparticle crosslinking polymer chains during polymerization.
  • Polymerization can be initiated from the surface of the clay particles due to their high cationic exchange capacity.
  • employed in the ink formulation may exhibit increased stretchability and strength compared to covalently-crosslinked hydrogels formed without clay.
  • the concentration of the clay particles is about 20 wt.% or less or about 10 wt.% or less, and typically is at least about 5 wt.%. Concentrations of clay within this range may yield printed hydrogel filaments that can flow and retain their shape as desired.
  • the clay particles may comprise synthetic hectorite clay, which is commercially available from Southern Clay Products, Inc. as Laponite XLG.
  • oxygen-scavenging enzyme in the ink formulation may drastically improve polymerization.
  • Oxygen inhibition which refers to the oxygen-induced inhibition of curing in polymers undergoing free-radical polymerization, can be a major challenge in the 3D printing of hydrogel-based inks.
  • a hydrogel composite filament may include hundreds of microns or more of poorly cured surface gel.
  • An oxygen-scavenging enzyme such as the naturally occurring glucose oxidase, can dramatically improve the
  • the oxygen scavenging enzyme is present in the hydrogel composite ink formulation at concentration in the range of from about 0.1 wt.% to about 10 wt.%.
  • the ink formulation may include an oxygen scavenging enzyme in an amount of at least about 0.1 wt.%, or at least about 1 wt.%, and typically no more than about 10 wt.%, or no more than about 8 wt.%.
  • an oxygen scavenging enzyme in an amount of at least about 0.1 wt.%, or at least about 1 wt.%, and typically no more than about 10 wt.%, or no more than about 8 wt.%.
  • glucose oxidase glucose oxidase
  • glucose is further included in the ink formulation, the glucose may be present at a concentration of from about 1 wt.% to about 40 wt.%.
  • Exemplary monomers that may be suitable for the hydrogel composite ink formulation include one or more of the following: N,N- dimethylacrylamide (DMAm), N-isopropylacrylamide (NIPAm), and sodium acrylate.
  • a monomer comprising an acrylamide or an acrylate may be physically crosslinked by the clay particles during polymerization, as described above, and also exhibits significant swelling when exposed to water.
  • the monomer(s) are present in the ink formulation at a concentration in the range of from about 1 wt.% to about 30 wt.%.
  • the concentration of monomer in the composite ink formulation may be at least about 1 wt.%, at least about 5 wt.%, or at least about 10 wt.%.
  • the concentration of monomer in the composite ink formulation is no greater than about 30 wt.%, no greater than about 25 wt.%, or no greater than about 20 wt.%.
  • the monomer may in some cases be polymerized to form a stimuli-responsive polymer that can exhibit reversible shape change behavior.
  • Such monomers may be referred to as stimuli-responsive monomers, and monomers that do not form stimuli- responsive polymers may be referred to as nonresponsive monomers.
  • a 4D printed structure comprising a stimuli-responsive polymer may return to a contracted configuration (e.g., the initial printed configuration or configuration prior to swelling) upon exposure to a suitable stimulus, such as a change in temperature, light, or pH.
  • a stimulus that may be localized to a portion of the 4D printed structure may lead to partial or localized deswelling of the structure.
  • NIPAm may be polymerized to form poly(N- isopropylacrylamide) (PNIPAm), which can undergo a thermoreversible shape change. Accordingly, after hydration under ambient conditions, a hydrogel composite filament comprising a PNIPAm matrix may be
  • the swollen or 4D printed configuration may be obtained again simply by reducing the water temperature.
  • FIGs. 7A-7D show a reversible, temperature-induced shape change of a 4D printed flower structure composed of a PNIPAm hydrogel matrix including cellulose fibrils (0.8 wt.%).
  • the flower structure maintains the swollen configuration in room temperature water, as shown in FIGs. 7A-7B, but upon exposure to a 50°C warm water bath, the hydrogel matrix contracts and substantially returns to the initial, 3D printed planar configuration, as shown in FIGs. 7C- 7D.
  • the transformation can be cycled back and forth by changing the water temperature, where heating leads to contraction and cooling leads to swelling.
  • the shape change is believed to be due to the coil-to-globule transition of the PNIPAm.
  • a reversible shape change may be achieved in a hydrated 3D printed structure by the application of heat or light (e.g., infrared (IR) light).
  • heat or light e.g., infrared (IR) light.
  • the same stimuli- responsive clay-based hydrogel as used in FIGs. 7A-7D is used in this example; however, single-walled carbon nanotubes are employed as the anisotropic filler particles instead of cellulose fibrils.
  • the reversal with heat is very rapid due to the increased thermal conductivity afforded by the carbon nanotubes (0.4 wt.% in this example) in the hydrogel.
  • carbon nanotubes exhibit light absorption properties that can be exploited for shape reversal.
  • the carbon nanotubes can absorb IR energy and convert it to heat, thereby activating a phase change transition of the PNIPAm, it is possible to achieve shape reversal by exposing the hydrated hydrogel composite to IR radiation.
  • Other types of anisotropic filler particles such as graphene, gold particles, and carbon fibers, may also exhibit photothermal behavior, where excitation of the particles by light leads to local heat emission.
  • Such structures may be useful for transformative electronics or photonics, as well as for bioelectronic applications, where the conductivity of the anisotropic filler particles may enable electrical signaling of cells such as neurons and/or muscle cells.
  • the entire 4D printed structure is exposed to the stimulus (e.g., temperature or light) in order to effect shape reversal. It is also possible to expose only a portion of the structure to the stimulus in order to induce a localized deswelling of the filaments. For example, if only a portion of a hydrogel matrix (e.g., pNIPAm reinforced with photothermally active carbon fibers) is exposed to laser light, such that only a fraction of the carbon fibers increases in temperature, then the deswelling of the filaments may be localized to the area of laser heating.
  • a hydrogel matrix e.g., pNIPAm reinforced with photothermally active carbon fibers
  • Carbon fibers may be especially useful as photothermal
  • pitch-derived carbon microfibers exhibit broad light absorption, high stiffness (e.g., about 900 GPa) and an aspect ratio of greater than 20.
  • Their microscale dimensions e.g., 5-15 microns in diameter and 100-300 microns in length, typically) facilitate direct
  • the hydrogel composite filaments may be seeded with cells, e.g., with a plurality of one or more types of cells.
  • the seeding may occur before or after deposition of the filaments.
  • the cells may be incorporated into the composite ink formulation prior to depositing the hydrogel composite filaments.
  • the seeding may be carried out after deposition, polymerization, hydration, and/or shape reversal (contraction) of the filaments.
  • Carrying out the seeding post-polymerization may be advantageous to ensure that the cells are not exposed to unreacted monomer or clay particles, which may be detrimental or toxic to the cells.
  • Cell seeding may be carried out after deposition using a suitable cell culture medium and techniques known in the art.
  • it may be advantageous to produce the hydrogel composite filaments from a hydrogel that does not contain clay or from another suitable material, such an extracellular matrix material as set forth in PCT/US2014/063810.
  • hydrogel composite filaments may contain hydroxyapatite particles and/or another type of bioactive particle (e.g., as the anisotropic filler particles).
  • a stimuli-responsive 4D printed flower structure comprising hydrogel composite filaments is seeded with cells.
  • the hydrogel composite filaments include a PNIPAm hydrogel matrix and cellulose fibrils embedded therein.
  • the hydrated flower is first coated with fibronectin (a common protein used to increase cell adhesion), and equilibrated at 37 ° C, which transforms the flower to the flat
  • the cells green fluorescent protein (GFP) expressing fibroblasts
  • GFP green fluorescent protein
  • This seeded hydrogel composite structure is fixed and stained after 10 days of culture to reveal the actin filaments within the cells.
  • the highly aligned nature of the actin filaments indicates the cells preferentially align and spread in the direction of printing, where the hydrogel composite filament is stiffest.
  • This approach may be used to interrogate cellular response in several ways. For example, the ability to actuate between shapes may facilitate investigating the role of curvature and geometry on cellular response. Volumetric expansion and contraction of the hydrogen composite structure may influence cell behavior, especially in cells that undergo these changes natively, as in muscles. In addition, the repetitive change in stiffness as a result of the swelling and deswelling of the hydrogel composite filaments could influence cell behavior, especially in stem cells and bone-lineage cells.
  • the anisotropic filler particles may exhibit a high stiffness to influence the swelling behavior of the hydrogel composite filament.
  • the filler particles may also or alternatively exhibit another functionality to impart a desired property to the hydrogel composite, such as electrical conductivity, bioactivity, photothermal activity and/or magnetic behavior.
  • the anisotropic filler particles may comprise cellulose, carbon, silicon, hydroxyapatite, a metal or alloy (e.g., Ag, Cu, Al, Au, Co, Cr, Ni, Pt, Sn, Ti, and/or Zn), an oxide (e.g., SiO 2 , AI 2 O 3 , TiO 2 , ZnO, SnO, ITO, BaTiO 3 , FeO 2 , and/or Fe 3 O 4 ) or another material having a desired property.
  • the anisotropic filler particles may take the form of, for example, fibers, fibrils, whiskers, platelets, microfibers, nanofibers, nanotubes and/or nanowires.
  • the anisotropic filler particles may comprise cellulose fibrils, carbon nanotubes, carbon fibers, and/or other high aspect ratio particles with a suitable combination of functional properties, stiffness and aspect ratio.
  • the concentration of the anisotropic filler particles in the composite ink formulation may be at least about 0.01 wt.%, at least about 0.04 wt.%, at least about 1 wt.%, at least about 5 wt.%, or at least about 10 wt.%.
  • concentration of the concentration of the anisotropic filler particles in the composite ink formulation may be at least about 0.01 wt.%, at least about 0.04 wt.%, at least about 1 wt.%, at least about 5 wt.%, or at least about 10 wt.%.
  • anisotropic filler particles may also be no greater than about 30 wt.%, no greater than about 20 wt.%, no greater than about 15 wt.%, or no greater than about 10 wt.%.
  • Stress-strain data obtained from 4D printed structures comprising a pNIPAm hydrogel matrix reinforced with up to 10 wt.% carbon fibers indicate that the elastic modulus (stiffness) as well as the mechanical anisotropy of the 4D printed structures increases with increasing
  • concentration of the anisotropic filler particles as shown in FIG. 8A.
  • the incorporation of stiff, anisotropic filler particles in the hydrogel matrix also leads to an increase in stretchability (e.g., up to 800%) of the 4D printed structures.
  • the anisotropic filler particles have an aspect ratio greater than 1 , where the aspect ratio may be defined as a length-to-width ratio. In some cases, the aspect ratio may refer to a length-to-thickness ratio. If the width and the thickness of a particle are not of the same order of magnitude, the term "aspect ratio" may refer to a length-to-width ratio. If the anisotropic filler particles are agglomerated, the aspect ratio relevant to the properties of the ink formulation and the hydrogel composite filament may be the aspect ratio of the agglomerated particles.
  • At least some fraction of, or all of, the anisotropic filler particles may have an aspect ratio greater than about 2, greater than about 5, greater than about 10, greater than about 20, greater than about 50, or greater than about 100.
  • the aspect ratio of the high aspect ratio particles is no greater than about 1000, no greater than about 500, or no greater than about 300.
  • Such high aspect ratio particles may be at least partly aligned during 3D printing of the ink formulation, depending in part on the size and aspect ratio of the particles in comparison to the diameter of the deposition nozzle.
  • the anisotropic filler particles may have at least one short dimension (e.g., width and/or thickness) that lies in the range of from about 1 nm to about 50 microns.
  • the short dimension may be no greater than about 20 microns, no greater than about 10 microns, no greater than about 1 micron, or no greater than about 100 nm.
  • the short dimension may also be at least about 1 nm, at least about 10 nm, at least about 100 nm, at least about 500 nm, at least about 1 micron, or at least about 10 microns.
  • the anisotropic filler particles may have a long dimension (e.g., length) that lies in the range of from about 5 nm to about 10 mm, and is more typically in the range of about 1 micron to about 5 microns, or from about 100 nm to about 500 microns.
  • the long dimension may be at least about 10 nm, at least about 100 nm, at least about 500 nm, at least about 1 micron, at least about 10 microns, at least about 100 microns, or at least about 500 microns.
  • the long dimension may also be no greater than about about 5 mm, no greater than about 1 mm, no greater than about 500 microns, no greater than about 100 microns, no greater than about 10 microns, no greater than 1 micron, or no greater than about 100 nm.
  • characteristic can be understood to be a nominal value for the plurality of particles, from which individual particles may have some deviation, as would be understood by one of ordinary skill in the art.
  • a first layer of filaments is deposited in a first predetermined arrangement on a substrate, and then a second layer of filaments is deposited in a second predetermined arrangement on the first layer of filaments.
  • Each of the filaments comprises a hydrogel matrix and
  • anisotropic filler particles embedded therein and thus may be referred to as a hydrogel composite filament.
  • the first and second layers are exposed to water, and the filaments of the first layer and the second layer swell in size while remaining in contact at the contact regions to form a curved 3D shape.
  • the method may entail depositing a layer of filaments in a predetermined arrangement on a flexible substrate, where the filaments contact the flexible substrate at one or more contact regions.
  • Each filament comprises a hydrogel matrix and a plurality of anisotropic filler particles embedded therein.
  • the flexible substrate may be a solid or porous substrate, such as a fabric comprising a plurality of natural and/or synthetic fibers. The layer is hydrated, and the filaments swell in size while remaining in contact with the flexible substrate at the one or more contact regions. Thus, the flexible substrate is forced to adopt a
  • the method may comprise depositing a first layer of filaments on a substrate in a first predetermined arrangement, and depositing a second layer of the filaments in a second predetermined arrangement on the first layer, where the filaments from the second layer contact the filaments from the first layer at a number of contact regions, and where each filament comprises a hydrogel matrix and a plurality of anisotropic filler particles embedded therein.
  • the first layer and the second layer are hydrated, and the filaments of the first and second layers swell in size while remaining in contact at the contact regions, thereby forming a curved three-dimensional hydrogel composite structure. After the hydrating and the swelling, the hydrogel matrix is exposed to a stimulus to induce deswelling of the filaments and shape reversal to a contracted configuration.
  • Extrusion-based 3D printing may be used to deposit the hydrogel composite filaments in the desired arrangements according to the print path of a deposition nozzle.
  • the hydrogel composite filaments may be formed from a hydrogel composite ink formulation by extrusion through a deposition nozzle.
  • the substrate for deposition may be rigid or flexible and typically comprises a material such as glass or another ceramic, PDMS, acrylic, polyurethane, polystyrene or another polymer.
  • flexible substrates may be solid or porous, and in some examples may comprise a fabric formed from a plurality of natural and/or synthetic fibers.
  • the substrate may not be a solid-phase material, but may instead be in the liquid or gel phase and may have carefully controlled rheological properties to support the deposited filaments.
  • the anisotropic filler particles undergo shear- induced alignment as the hydrogel composite ink is extruded through the nozzle.
  • the anisotropic filler particles embedded in the hydrogel matrix may be at least partially aligned - and in some cases highly aligned - with the longitudinal axis of each filament so as to generate anisotropic swelling behavior.
  • Printing experiments carried out using a composite ink formulation comprising microscale carbon fibers in a NIPAm hydrogel matrix elucidate the extrusion-driven alignment of the anisotropic filler particles that occurs during printing. Using a tapered deposition nozzle, the shear forces during extrusion gradually increase along the length of the nozzle, reaching a maximum near the nozzle outlet or exit.
  • the carbon fibers may transition from being partially aligned at an upstream location to highly aligned near the exit of the nozzle.
  • a translucent nozzle allows for direct imaging of the carbon fibers under flow. Images obtained during printing reveal that the deposited hydrogel composite filaments can retain a high degree of alignment in the direction of printing, independent of the print pattern.
  • the alignment of the anisotropic filler particles is a critical factor in generating anisotropic swelling behavior and elasticity in the printed hydrogel composite filaments.
  • the swelling of the hydrogel composite filaments may be greater along a transverse axis thereof than along the longitudinal axis, and swelling ratios of at least about 1 .2 or at least about 1 .5, and up to about 10, are possible. Higher
  • concentrations of anisotropic filler particles may lead to an increase in the swelling ratio - in other words, an increase in the ratio of the swelling strain along the transverse axis to the swelling strain along the longitudinal axis, as demonstrated by experiments with hydrogel composite filaments including carbon fibers.
  • the data of FIG. 8B show how the anisotropic swelling varies as a function of carbon fiber concentration and temperature, where very little anisotropy is obtained at the lowest carbon fiber
  • each contact region X may be understood to be an interfacial region between a portion of a filament from the first layer and a portion of a filament from the second layer.
  • the size of the interfacial regions prior to swelling may be determined largely by the width of the filaments as well as by the relative orientation of the filaments at each of the contact regions.
  • the relative orientation may be expressed as the angular offset ⁇ / between a filament from the first layer and a filament from the second layer at each contact region X,.
  • the method may further entail using a
  • Any curved surface may be described by a mean curvature (H) and a Gaussian curvature ( ) at any given point.
  • the mathematical model utilizes, as inputs, the curvatures (H, K) for the desired curved surface (which may be referred to as a 3D shape or structure elsewhere in this disclosure) along with the longitudinal and transverse swelling strains (a M and respectively) and the elastic moduli of the hydrogel composite filaments.
  • degree notation may be used to describe the orientation of each printed layer in reference to an orthogonal grid pattern that may be defined by the boundary or an axis of the printed arrangement of filaments.
  • the first number before the "I" represents the orientation of the top (second) layer with respect to the boundary/axis while the number after the "I” represents the orientation of the bottom (first) layer with respect to the boundary/axis.
  • the top layer is oriented at 90° with respect to the long axis of the petal, while the bottom layer is oriented at 0° with respect to the long axis of the petal.
  • All of the hydrogel composite filaments may comprise the same hydrogel matrix and anisotropic filler particles.
  • some or all of the hydrogel composite filaments may comprise a different hydrogel matrix and/or different anisotropic filler particles to achieve, for example, different swelling ratios or different functionalities in different filaments or layers.
  • the first layer of filaments may comprise a first hydrogel matrix and a first type of anisotropic filler particles
  • the second layer of filaments may comprise a second hydrogel matrix and/or second type of anisotropic filler particles different from those of the first layer.
  • the hydrogel matrix may be a hydrogel as described above or elsewhere in this disclosure, and the anisotropic filler particles may have any of the characteristics (composition, size, aspect ratio, etc.) set forth above or elsewhere in this disclosure.
  • the hydrogel composite filaments deposited in the above-described method may further have any of the characteristics (e.g., composition, swelling ratio, etc.) set forth in this disclosure for the composite filaments.
  • Each of the hydrogel composite filaments deposited on the substrate may be a single continuous filament of a desired length or may be formed from multiple extruded filaments having end-to-end contact once deposited.
  • a hydrogel composite filament of any length may be produced by halting deposition after the desired length of the filament has been reached.
  • the desired length of the hydrogel composite filament may depend on the print path and/or the geometry of the structure being fabricated.
  • a hydrogel composite structure (e.g., the lattice structure shown in FIG. 2A or 2B) may be described as including a number of filaments even though it may be possible to deposit the filaments in a continuous process without stopping and restarting.
  • the deposition nozzle may be moving with respect to the substrate during deposition (i.e., either the nozzle may be moving or the substrate may be moving, or both may be moving to cause relative motion between the nozzle and the substrate). Rotational motion of the nozzle is also possible to influence the alignment of the anisotropic particles, as described for example in International Patent Application No.
  • the method may further comprise, prior to exposing the filaments to water, polymerizing the hydrogel so as to form a crosslinked hydrogel, thereby increasing the mechanical robustness of the filaments.
  • the polymerization may be effected by light (e.g., UV light), heat, or a chemical, and may be aided by the presence of clay particles and/or an oxidation inhibitor (e.g., glucose oxidase and/or glucose) in the uncured hydrogel composite filament.
  • an oxidation inhibitor e.g., glucose oxidase and/or glucose
  • the hydrogel matrix may be more "sticky” and malleable, which can be conducive to forming a good bond between the layers at the contact regions X,. It is also possible, however, for the polymerization to be carried out during deposition of the filaments, or in separate steps after deposition of each layer.
  • hydration of the filaments to induce swelling may be carried out by exposing the layer(s) to water or an aqueous solution by dipping, immersion, spraying, or another deposition method.
  • the hydrating may also or alternatively entail exposing the filaments to a humid gaseous environment, such as an air environment having a humidity of at least about 40%, or at least about 60%.
  • a humid gaseous environment such as an air environment having a humidity of at least about 40%, or at least about 60%.
  • room temperature water e.g., about 20°C-25°C
  • the extent of anisotropic swelling of the hydrogel composite filaments depends strongly on the orientation of the filler particles within the hydrogel matrix.
  • the anisotropic filler particles may be understood to be "at least partially aligned" with the longitudinal axis of the 3D printed hydrogel composite filament if at least about 25% of the anisotropic filler particles are oriented such that the length or long axis of the filler particle is within about 40 degrees of an imaginary line extending along the longitudinal axis of the composite filament. This imaginary line may also coincide with the print direction or print path.
  • the long axis of at least about 30%, at least about 35% or at least about 40% of the anisotropic filler particles may be oriented within about 40 degrees of the imaginary line.
  • the anisotropic particles may be understood to be "highly aligned" with the longitudinal axis of the 3D printed hydrogel composite filament if at least about 50% of the high aspect ratio particles are oriented such that the length or long axis of the filler particle is within about 40 degrees of an imaginary line extending along the longitudinal axis of the composite filament. This imaginary line may also coincide with the print direction or print path.
  • the long axis of at least about 60%, at least about 70%, at least about 80%, or at least about 90% of the anisotropic filler particles may be oriented within about 40 degrees of the imaginary line.
  • hydrogel composite filaments having at least about 25% of the anisotropic filler particles oriented such that the length or long axis of each filler particle is within about 20 degrees of the imaginary line described above, or within about 10 degrees of the imaginary line.
  • at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90% of the anisotropic filler particles may have a long axis oriented within about 20 degrees or within about 10 degrees of the imaginary line.
  • the above-described partial or high alignment of the anisotropic filler particles with respect to the longitudinal axis of the hydrogel composite filament may occur over an entire length of the filament or over only a portion of the length (e.g., over a given distance or cross-section).
  • An exemplary procedure for creating 4D printed architectures involves preparing an ink formulation including clay, monomer, anisotropic filler particles (e.g., cellulose fibrils (nanofibrillated cellulose) or carbon fibers), photoinitiator, enzyme/glucose, and deionized water.
  • architectures are printed at room temperature in air, and UV cured after print completion. Samples are immersed in deionized water to allow for swelling and shape transformation.
  • Exemplary hydrogel composite ink formulations are prepared as follows. Nanofibrillated cellulose (NFC) or raw milled carbon fiber (CF) powder (Dialead K223HM, Japan) is diluted from a stock solution to deoxygenated water under nitrogen flow, and mixed thoroughly using a Thinky mixer (ARE-310, Thinky Corp., Japan) in a closed container. Laponite XLG clay is then added under nitrogen flow and mixed again using the Thinky mixer. N,N-dimethylacrylamide (DMAm) (Sigma Aldrich, unmodified) is added to this anisotropic filler particle-clay solution under nitrogen flow and mixed again using the Thinky mixer.
  • NFC Nanofibrillated cellulose
  • CF raw milled carbon fiber
  • Irgacure 2959 (BASF), is added as the UV photonitiator.
  • D-(+)-glucose (Sigma Aldrich) and glucose oxidase (from Aspergillus niger, Sigma Aldrich) are added as oxygen scavengers.
  • the ink is hand mixed, followed by mixing using the Thinky mixer.
  • 1 vol.% of a 5 mg/mL solution of a monomeric rhodamine dye (PolyFluor570 - Methacryloxyethyl thiocarbonyl rhodamine B, Polysciences Inc.) is added under nitrogen flow and mixed using the Thinky mixer.
  • the ink Under nitrogen flow the ink is loaded into a syringe barrel and centrifuged to remove bubbles.
  • the final concentrations of each component are as follows for one exemplary ink formulation: 77.6 wt.% deionized water, 0.73 wt.% NFC, 9.7 wt.% Laponite XLG clay, 7.8 wt.% DMAm, 0.097 wt.% Irgacure 2959, 0.23 wt.% glucose oxidase, 3.8 wt.% glucose.
  • the ink is then mounted to the printer and attached to a controlled air pressure input (Nordson EFD Inc.). Via luer-lock connection, a variety of commercial nozzles of varying diameter (Nordson EFD Inc.) can be attached. All nozzles are stainless- steel, straight tips, or tapered plastic tips with 10 mm nozzle lengths.
  • B. Printing procedure Print paths are generated via production of G-code which outputs the XYZ motion of the 3D printer (ABG 10000, Aerotech Inc.). G-code is generated either by hand, using MeCode python scripting (Jack Minardi (Voxel8), Daniel Fitzgerald (WPI)), or by scripting in Mathematica (Wolfram Research). Samples are printed on glass slides covered with a Teflon adhesive film (Bytac, Saint-Gobain) and cured for 200 s using an Omnicure UV source (Series 2000, Lumen Dynamics Inc.). After curing, the printed architecture is coated in a thin film of Dl water to remove from the substrate.
  • C. Characterizing Alipnment and Swelling To test NFC alignment, unidirectional, solid-infilled samples are printed with various sizes of nozzles (150 -1500 ⁇ diameter). NFC filled and unfilled cast hydrogel samples are also fabricated for comparison. Longitudinal (print direction) and transverse strains are calculated by measuring sample dimensions as-fabricated and after reaching equilibrium swelling in Dl water, or approximately 5 days. These samples are then stained via immersion in 5 ml_ of a 0.1 mg/mL solution of Calcofluor White (Sigma Aldrich), with 200 ⁇ _ of 10 wt.% potassium hydroxide solution added, for 24 hours.
  • Calcofluor White Sigma Aldrich
  • D. Mechanical testing Tensile specimens are prepared via printing and curing. The print path of transverse and longitudinal orientations are shown in FIG. 9. Samples are tested either immediately after fabrication or after soaking in Dl water for 5 days. Deswollen samples are tested after equilibrating in a 37°C incubator for an additional three days. The samples are tested on an Instron mechanical testing machine (Model 3342) with a 10 N or 50N load cell at a rate of 100 mm/min until failure. Stress and strain are calculated via initial specimen dimensions. Moduli are calculated from linear regions of the stress-strain curves (less than 20% strain).
  • E. Rheological Characterization Ink rheology is characterized via testing on a rheometer (DHR-3, TA Instruments) with a 40 mm diameter, 2.005° cone-plate geometry. Flow experiments are conducted via a logarithmic sweep of shear rates (0.1-1000 1/s). Oscillation experiments are conducted via a fixed frequency of 1 Hz and oscillatory strain of 0.01 , with a sweep of stress (0.1-3000 Pa). All experiments are performed in ambient conditions with a gap height of 56 ⁇ and preliminary soak time of 60 s.
  • F. Macro Imaging Photographic images of pNIPAm-NFC hydrogel composite samples are taken under a broad spectrum UV light source to excite the rhodamine dye in the ink. Images of pNIPAm-CF hydrogel composite samples are taken in bright field without dye. Images are taken with DSLR cameras (Mark III or Rebel T3i, Canon Inc.) with a variety of lenses, or with a Keyence Zoom microscope (VHX-2000, Keyence, Japan). As-printed specimens are photographed in ambient conditions, while resulting shape transformations are captured in an acrylic enclosure containing deionized water.
  • curvatures the two invariants associated with the curvature of any surface.
  • positive Gaussian curvature can be generated by swelling concentric circles.
  • the structure is conical (K ⁇ 0) far away from the tip, but has Gaussian curvature K ⁇ e lh 2 concentrated near the apex.
  • almost uniform negative Gaussian curvature associated with saddle-like shapes may be obtained from an orthogonal bilayer lattice that swells orthogonally, as shown in Fig. 10B.
  • each layer yields a surface that is curved oppositely along two directions, i.e., a saddle-shaped surface with mean curvature H ⁇ 0 and Gaussian curvature Combining these two morphologies produces a 4D printed sample with zones of both positive and negative Gaussian curvature, as shown in FIG. 10C.
  • Overlapping circular arcs generate a structure that transitions from swelling primarily perpendicular to the spine of the petal to swelling primarily parallel to the border, leading to a surface with varying K.
  • This structure exhibits negative Gaussian curvature, which increases towards the edge.
  • breaking translational symmetry across the midplane and replacing it by reflection symmetry yields a ruffled structure, while breaking the reflection symmetry yields a helicoid.
  • 4D printing allows control over the curvatures of both solid (infilled) structures and lattice-based structures with varying porosity (or filament spacing).
  • petals By combining patterns that generate simple curved surfaces, a series of functional folding flower architectures are created to demonstrate the capabilities of 4D printing.
  • petals re printed in a floral form, as shown in FIG. 1 1 A, comprised of a bilayer lattice with a 90°/0° orientation, similar to prior bilayer strips.
  • an identical pattern is printed using an ink devoid of microfibrils, and it is observed to remain flat upon swelling.
  • the petals are printed with the ink filaments of the bilayer in a -45°/45° orientation, as shown in FIG.
  • these constructs contain spanning filaments that are readily fabricated by direct writing of the viscoelastic composite ink.
  • the interfilament spacing promotes rapid uptake of water through the filament radius (-100 ⁇ ), leading to shape transformations that occur on the order of minutes, consistent with diffusion-limited
  • Reversal of the swelling of the PNIPAm matrix can also be effected by light exposure (e.g., IR radiation) when the anisotropic filler particles include carbon nanotubes in addition to or instead of the cellulose fibrils used in the previous example, as discussed above in reference to FIGs. 7E-7H.
  • the 4D structure is obtained after 3D printing composite ink filaments in a 90°/0° bilayer and swelling in room temperature water (FIGs. 7E-7F). Reversal of the swelling occurs at an elevated water temperature or upon exposure to IR radiation (FIGs. 7G-7H).
  • the complex shape of the orchid Dendrobium helix may be reproduced by encoding multiple shape changing domains.
  • the print path is designed with discrete bilayer orientations in each petal.
  • the resulting 3D morphology following swelling in water resembles the orchid and exhibits four distinct types of shape change (three different petal types and the flower center), based on configurations demonstrated in FIG. 10B-10C and FIGs. 1 1A-1 1 B.
  • Harnessing anisotropic swelling can allow for precise control over curvature in bilayer structures. As discussed above, differential swelling between the top and bottom layers of a bilayer system can induce curvature if the layers are forced to remain in contact along the entire midplane.
  • Quantifying the curvature induced in bilayer structures as a consequence of anisotropic swelling may utilize a mathematical model for the mechanics of anisotropic plates and shells.
  • Such a model combines aspects of the classical Timoshenko model for thermal expansion in bilayers with a tailored metric-driven approach that employs anisotropic swelling to control the embedding of a complex surface.
  • a mathematical model may also be employed to solve the inverse problem, that is, how to determine, based on a desired 3D curved shape, the requisite arrangement of hydrogel composite filaments in each layer of the bilayer structure - and thus the two-layer print path - in order to achieve the desired 3D curved shape upon swelling. More specifically, a suitable mathematical model can identify the predetermined angle ⁇ i for each contact region X, between the layers as well as a suitable spacing between the filaments in each layer.
  • anisotropic particles having a bottom layer oriented along the e x direction and the top layer rotated by ⁇ degrees counterclockwise.
  • the height of each layer and the total height can be tuned by nozzle size, and the "effective thickness" of the bilayer is influenced by the filament spacing.
  • the swelling ratio can be tuned by controlling the composition and structure of the hydrogel composite filaments - e.g., the amount of clay, the type and amount of the anisotropic filler particles, the degree of alignment of the anisotropic filler particles, and the properties of the hydrogel matrix (e.g., how much the polymer tends to swell).
  • ink may be treated as an orthotropic elastic material, which satisfies the stress-strain relationship (throughout the standard Einstein
  • the strain tensor in a thin film is given by where z is the distance is the distance from the interface and
  • the stress tensor is related to the curvature through the bending moments
  • the longitudinal and transverse Youngs moduli are, in one example, and the shear modulus is
  • the ratio of interlayer thicknesses is believed to be crucial to determining the sign and magnitude of the resulting curvature for these structures.
  • an effective thickness based on variable interfilament spacing is invoked to achieve local gradients in curvature. Since each layer contains a fixed volume of the deposited ink, the effective thickness may be given by the volume of the deposited ink divided by the cross-sectional area. This approach is consistent with the resulting porous structures, as the curvature is slowly varying depending on the level of filament diameter and
  • FIGs. 13A-13E it is possible to begin with a desired 3D shape, such as the calla lily shown in FIG. 13A, provide a mathematical model of the 3D shape, and use the mathematical model to extract the desired curvatures and design a suitable print path and arrangement of filaments in each layer.
  • a desired 3D shape such as the calla lily shown in FIG. 13A
  • solve the inverse problem uses the mean and Gaussian curvatures to determine the proper inputs for the printing process (e.g., the filament arrangement or print path, the height and thus nozzle size, and the overall boundary size and shape).
  • the details of the inverse problem to find print paths for a given target surface are described in detail below.
  • the mathematical model enables the translation of a complex three-dimensional surface (e.g., see FI . 13B) described by the equation
  • the streamlines of this field may be integrated to generate the print path for the first layer.
  • the print path for the second layer may then be obtained by adding the two fields

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Abstract

L'invention concerne un procédé d'impression 4D comportant les étapes consistant à déposer une couche de filaments dans un agencement prédéterminé sur un substrat souple. Chaque filament comporte une matrice en hydrogel et une pluralité de particules de remplissage anisotropes enrobées dans celle-ci. Les filaments sont en contact avec le substrat souple dans une ou plusieurs régions de contact. La couche de filaments est hydratée et les filaments se dilatent tout en restant en contact avec le substrat souple au niveau des régions de contact. Le substrat souple est ainsi amené à adopter une forme incurvée prédéterminée.
PCT/US2016/063918 2015-11-30 2016-11-29 Formulation d'encre composite avec hydrogel et procédé d'impression 4d d'une structure composite avec hydrogel WO2017095773A1 (fr)

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